Session T3D PORTABLE NETWORKING LABORATORY Stephen Fitzhugh1 , Lynn DeNoia 2 , Roger H. Brown3 , and Christopher Fitzhugh4 Abstract This paper describes a portable networking laboratory composed of PC-based servers and Layer 2/3 switches. The laboratory is self-contained and mounted in a portable rack to facilitate network demonstrations and hands-on learning in most classrooms. The portable laboratory is a cost-effective solution to providing access to network equipment for hands-on experience with networking protocols in an isolated environment. Supporting system software includes Linux and FreeBSD. Applications software includes Extreme Network's EPICenter network management software. We provide details on the hardware configuration and network topology. Examples of laboratory exercises or experiments using the portable lab are described. The portable labs are used to reinforce concepts presented in a variety of networking courses, from the introductory course that teaches network fundamentals to the capstone course in network management. Index Terms computer networks, network laboratory, network management
INTRODUCTION The ubiquity of computer networks in business, as well as the prospects of a lucrative career as a networking professional, make computer networking courses very popular among students in computer science and computer engineering. Courses are offered in basic computer communication systems, local area networks, network analysis and design, and network management, to mention a few. Students can complete a certificate program or earn a graduate degree in computer networking, however, without ever touching an Ethernet switch or a router. Lack of physical space to construct, and financial resources to outfit, a networking laboratory impede efforts to introduce handson network experience. We describe a portable networking laboratory for providing practical experience in our graduate networking courses offered at Rensselaer at Hartford. Rensselaer at Hartford is a branch campus of Rensselaer Polytechnic Institute that serves businesses in southern New England by providing opportunities for working professionals to earn Master's degrees in Engineering, Computer Science, and Management. Each course meets one night per week to accommodate work schedules.
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Many students will learn more, or learn more quickly, "by doing". Kolb's [1] research indicates that the learning style of working professionals tends toward convergers and accommodators, using active experimentation to reinforce the learning experience. Laboratory exercises enrich the learning process by facilitating concrete experiences to reinforce abstract concepts in support of these learning styles. Students have an opportunity to use networking tools in a "crashable" network that is isolated and separate from the campus-wide network. Separation is necessary since our network administrators and technical support staff do not want faculty or students monitoring, controlling, adjusting, testing, or fixing anything on the campus-wide network. We share the laboratory across the breadth of our networking curriculum. In a graduate class, networking demonstrations or exercises are not needed every time the class meets. Portable units simplify scheduling for laboratory time, obviating the need for a dedicated facility. Each portable unit consists of two Layer 2/3 switches and a PC-based server mounted in a network rack on casters to facilitate portability for use in classrooms to demonstrate networking protocols and to provide access to observable performance metrics. A laptop is used as the network management station. Student laptops can be connected as network hosts to generate network traffic through file transfers and access to other network services. Two portable units can be interconnected to extend the network size and to generate network traffic when student laptops are not used. We begin by briefly describing the hardware and network architecture, the supporting system, and application software. Then we explore each graduate course and offer a description of experiments, exercises, or demonstrations that will be used with the portable networking laboratory. This represents the beginning of our educational network laboratory and we describe opportunities for future growth and expanded utility of our lab.
HARDWARE CONFIGURATION The core of the portable networking laboratory is a pair of Extreme Network Summit 48 switches that perform both layer 2 (data link) and layer 3 (network) switching. These switches can be configured into Ethernet Virtual Local Area Networks (VLANs), as well as establishing multiple domains for implementing the Layer 3 routing capabilities. Once the switch has been initially configured, further
Stephen Fitzhugh, Rensselaer At Hartford, Dept. of Engineering & Science, 275 Windsor St, Hartford, CT, 06120,
[email protected] Lynn DeNoia, Rensselaer At Hartford, Dept. of Engineering & Science, 275 Windsor St, Hartford, CT, 06120,
[email protected] Roger H. Brown, Rensselaer At Hartford, Dept. of Engineering & Science, 275 Windsor St, Hartford, CT, 06120,
[email protected] Christopher Fitzhugh, Worcester Polytechnic Institute, Worcester, MA 01609,
[email protected]
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Session T3D configuration changes can be made using a web browser on a network host. Teaching assistants or student volunteers are a valuable source of administrative support, especially while conducting laboratory exercises. A server running a UNIX-like [2] operating system provides application-layer services, such as file transfer (ftp and tftp), remote access (telnet and ssh), dynamic host configuration (dhcp), domain name service (dns), and access to network tools, such as tcpdump and netstat. Apache Web servers provide access to materials required by the students to conduct laboratory measurements and observations. Faculty user accounts provide storage space for laboratory support materials and at least one guest user account provides access for students. Individual student accounts can be created on the server to provide storage space for laboratory data for the semester, incurring additional administrative overhead. SAMBA [3] provides file sharing services to Windows-based hosts. An advantage of using UNIX-like operating systems, such as Linux and FreeBSD, is the wide range of network analysis tools, such as tcpdump and netstat, available within those distributions. The tcpdump utility allows students to observe network traffic and capture information about frames that match a particular criteria. Other utilities that are discussed in lectures, such as ping, netstat, and ifconfig, can be experimented with to observe network information and test the performance characteristics of the portable network. On Windows-based host, the ipconfig utility can be used to display the host network configuration information.
Godel 192.168.0.3 Erlang 192.168.0.6
Layer 2/3 Switch 192.168.0.1
Laptop Dynamic Address
EPICenter client runs in a Java-enabled browser. Student laptops connected as hosts complete the network. A typical network configuration is shown in Figure 1. IP addresses of all connected network devices are chosen from addresses reserved for private networks. IP addresses of the student laptop computers can be statically assigned within each domain or dynamically assigned using a DHCP server to simplify network configuration for the lab exercises. Laptop network configuration information must be preserved to restore the configuration after connection to the portable laboratory.
NETWORK M ANAGEMENT A network management system (NMS) is a set of applications and tools that help networking personnel (the students) observe the behavior of the network and extract information that will assist in configuration, fault, performance, and security management. Our NMS is SNMPbased. That is, the protocol used for the exchange of management information to/from the centralized NMS and the remote routers, switches, hosts, and other agents (SNMP engine entities) is based on the SNMP standard protocols. By focusing on the SNMP protocol and the corresponding standard Management Information Base (MIB) managed objects, the students will be exposed to standard nonproprietary solutions. Once a student has been exposed to the fundamental exchange of SNMP messages that carry standard MIB objects between “managers” and “agents” we believe the student is then better prepared to understand the power of commercial NMS solutions. Common UNIX-based NM commands, e.g. ping, tcpdump, traceroute, snmpsniff, are used to explore network operations. In addition, we currently run Extreme Networks' Epicenter Network Management software for managing the network switches used in the portable lab. The Extreme Networks' EPICenter network management client runs in Internet Explorer in Windows. Our future plans include operational experimentation with Aprisma-Spectrum Software and other commercial NMS packages.
COURSE SUPPORT
172.16.0.1 NMS 172.16.0.10 Layer 2/3 Switch Laptop Dynamic Address
FIGURE 1 P ORTABLE LABORATORY NETWORK T OPOLOGY
All hardware is mounted in a standard network rack on casters for portability. Two racks can be linked together to increase the laboratory network to four switches and two servers. ExtremeWare's EPICenter network management software server and client is run on a Windows-based laptop and serves as the network management station. The
The portable networking lab supports the core group of networking courses by providing students with the opportunity to gain hands-on experience with network hardware to promote better understanding of the abstract concepts of computer networking taught in lectures. A brief description of the networking courses follows. Computer Communication Networks
The Computer Communication Networks (CCN) course is the introductory course in computer networks, covering the fundamental principles of digital communications, networking protocols, and an overview of currently implemented network technologies. The course emphasizes that modern networks must be designed to support a wide 0-7803-7444-4/02/$17.00 © 2002 IEEE November 6 - 9, 2002, Boston, MA 32 nd ASEE/IEEE Frontiers in Education Conference T3D-8
Session T3D range of applications. The view of the network as a provider of services to applications is developed, leading to the concept of layered architectures. Fundamental concepts of network architecture, proceeding from the physical to the network layer, are discussed in detail. The implementation of these concepts is discussed in the context of key networking architectures including traditional telephone network, X.25, Frame Relay, TCP/IP, and ATM. Students enrolled in this course are pursuing degrees in either Computer Engineering, Computer Science, or Information Technology. CCN can be used by students in Computer Science or Information Technology to satisfy a hardware-oriented course elective. Students enroll in CCN with diverse backgrounds, many without extensive technical preparation, and in many cases, CCN will be the extent of their contact with core networking equipment. For those students who take CCN to fill a hardware course requirement, the networking laboratory may be their only opportunity to obtain hands-on experience with network hardware and protocols. Topics that students explore using the portable networking laboratory include: • LAN standards, including host configuration and switching. • Network applications such as telnet for remote login and ftp for file transfers. • Functionality of individual network layers and their interaction. • TCP/IP details such as TCP and IP header contents, and Address Resolution Protocol in LANs. • Routing in packet switched networks using RIP and OSPF routing protocols. • Network performance analysis and management tools, including those that are available in the UNIX-like operating systems and those supplied by hardware vendors.
hosts, then use the ping utility to test reachability of other hosts. The accuracy of the parameters that they set is evidenced by the range of hosts with which they can communicate. The correct IP address and subnet mask allows communication with other hosts in their VLAN, but the correct default gateway is required to communicate with hosts outside of their VLAN. This exercise reinforces the concepts of LAN segmentation and subnetting. Once students have learned to correctly configure their host's network configuration parameters within the network laboratory environment, they are prepared to access tools to perform exercises designed to probe network design and performance issues. Guides to the exercises are made available by the Apache Web server so that exercises can be completed on a self-paced study basis to accommodate the diverse demographics of the class. Exercises that student may complete include: • TCP/IP headers: Students can observe packet headers of different network services by starting such tasks as retrieval of web pages, telnet and ftp sessions, and the ping utility. Students remotely login to the networking laboratory server using the telnet utility and capture header and content information of packets sent and received by the server using the tcpdump utility. The character string "tcpdump -x host erlang >> data.txt" is an example of a command line that will capture packet data and network parameters of packets of the server named "erlang" and write the information to a text file named "data.txt". Once the data has been captured, the student terminates the tcpdump utility and transfers the file to their laptop host. A text editor is used to examine packet headers in the text file for analysis. Students running Linux or FreeBSD on a laptop, or those with a Windows version of the tcpdump utility, can capture the packet header data directly to the laptop host for analysis. • ARP request/response: Applications using TCP/IP over LANs must translate the IP addresses of host or Students' first experience with the networking gateway devices on the LAN into hardware addresses laboratory is to configure their laptop computer to for the data link layer. Address Resolution Protocol communicate with the other network hosts. Many students in (ARP) performs this function through a request issued the course have experienced computer networks as they have by the initiating host and a response from the target the telephone system. In the telephone system, the telephone host. Students observe these interactions using the handset is the user interface that encapsulates the complexity tcpdump utility as above to capture the requests and of the telephone network, and is similar to the web browser responses. and electronic mail applications in the computer network • Packet timing: The tcpdump data contains timestamps domain. Since network configuration is typically performed for each packet recorded, providing the student with the by system administrators in the workplace, users do not have requisite information to calculate network throughput the opportunity to experiment with the network parameters. for file transfers for comparison to the throughput In the laboratory environment, one student laptop is formula presented in lectures. File sizes and network connected per switch port. Since the network switches cable lengths can be varied to observe the effects on the perform both layer 2 (data link) and layer 3 (network) throughput. switching, the switch ports are grouped into multiple virtual • Switch configuration: Students are able to use a web LANs (VLANs) to demonstrate subnetting. Students must browser to view the switch configuration since the configure their IP address, subnet mask, and default gateway Extreme Networks switches include browser client parameters to establish communications with other network support. Precautions must be taken to prevent students 0-7803-7444-4/02/$17.00 © 2002 IEEE November 6 - 9, 2002, Boston, MA 32 nd ASEE/IEEE Frontiers in Education Conference T3D-9
Session T3D
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from being able to execute changes to the switch configuration. Some configuration changes can render the switch inoperable until the configuration is restored. Configuration scripts that can be uploaded to the switch using tftp are extremely helpful while conducting laboratory exercises. Routing tables: The switch RIP and OSPF routing information can also be viewed by students using a web browser client as above. Multiple connections between switches with different IP domains can be used to illustrate the changes to the routing tables in the event that one of the connections is disabled.
Depending on the availability of laptop computers, students may choose to conduct the networking exercises working individually or in teams of two or three. LANs, MANs and Internetworking The LANs, MANs, and Internetworking (LMI) course is a graduate-level, advanced course in computer networking that provides additional depth in LAN/MAN technology, newly emerging technologies and applications, and the TCP/IP suite of protocols. Students use this course as an elective for Computer Engineering, Computer Science, or Information Technology programs. The Computer Communication Networks course above is a prerequisite. Course objectives include developing an understanding of how the protocols and technologies work, various application requirements on the network, general network design principles, and an appreciation for performance characteristics. It is highly desirable to enhance the study of topics such as routing, virtual LANs, and performance characteristics with a practical understanding of how the parameters affect network operations. We use simulation tools to study the overall network impact of number of users, underlying data link technology, and a mixed application environment. The portable networking laboratory provides an opportunity for hands-on experience in setting, and observing the effects of, specific parameters that require far too much detail to do effectively in a simulation study. Students bring laptop computers to class, connect them to the portable network (with suitable coaching in operating system set-up), and run applications to generate traffic with the network servers. The network management software installed on an instructor machine shows that traffic flows appropriately according to configured VLANs, routing access controls, and routing protocols. Students are guided to change switch parameter values and observe the effects on network traffic. Typical concepts that students learn in practice to reinforce their understanding of the theory include: • How much traffic 10 Mbps Ethernet can support without excessive delay (often a surprise when they know that most enterprises are installing at least 100 Mbps to the desktop);
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VLANs can effectively divide traffic to provide closed user groups where the traffic within the group cannot be viewed by non-members; Which routing parameters must have consistent values throughout the network in order for traffic to be forwarded properly; and How long it takes for the routing tables to converge following a link or switch failure. Network Management
Network Management (CISH-6230) is a capstone course and, if scheduling permits, should be taken as the third or fourth course in computer networking. This course looks at the essential aspects of monitoring, controlling and managing a significantly large enterprise network. The course begins with the five functional areas of network management: Fault, Configuration, Accounting, Performance, and Security Management. We introduce the TCP/IP or internet network management protocols SNMPv1, v2, v3, followed by the structure of network management information with MIBs (Management Information Base), and web-based management. The portable network lab is a perfect learning environment that allows a student to experiment with the retrieval and modification of management information. With SNMP-based management, the protocol for retrieving a managed object instance is Simple Network Management Protocol versions 1, 2, and 3. The definition of relevant management information, events, and other managed objects are specified in an adapted sub-set of the Abstract Syntax Notation One (ASN.1) language. A collection of standard managed objects is published in one or more documents called Management Information Base (MIB) specifications. Specifically MIBs are publicly available RFCs (Request for Comments) published by the IETF (Internet Engineering Task Force). Often this is the student’s first exposure to abstract syntax notation and the portable network lab offers the “reality” exposure to solidify the specification and use of a manged object. MIB specifications are dry reading – yet everything is properly defined, syntax, datatype, default values, textual description and unique object ID(OID). At least four concepts need to be explored by the student of network management. • The abstract definition of a managed object is documented in ASN.1, encoded in a frame using Basic Encoding Rules (BER) and ultimately sent as a string of octets or bytes. Can the student follow the transformation and encapsulation of messages from the abstract to the real byte implementation? • The collection and presentation of performance statistics and traffic flows. Performance data are accessed via Remote Monitoring (RMON) MIBs implemented in remote agents.
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The configuration of filters, alarms, and other event notifications to assist the performance and fault management of a network. The configuration of administrative keys for secure (secret and authenticated) exchange of SNMPv3 messages.
The above concepts can be explored using a MIB browser. A MIB browser refers to a generic management application that is used to query an agent for one or more MIB variables, and display those variables to the user for analysis and possible modification. MIB browsers are available in both web-based or command line interfaces. In either case, the Object ID and managed object value or instance is displayed to the user. With the help of the LINUX/FreeBSD tool snmpsniff a student can capture SNMP packets or messages going across the network and store them for further analysis.
FUTURE WORK
resulting in a better understanding of network operation, performance, and management. We provide examples of laboratory exercises and identify graduate courses that benefit from the lab support.
ACKNOWLEDGMENT We would like to acknowledge the contributions of the following individuals and companies: Farooque Mesiya and C-Cor, Inc. for the portable racks; Extreme Networks for the switches and network management software; and Jane Philion for the PC used for the FreeBSD server.
REFERENCES [1]
Kolb, David A., Experiential Learning: Experience at The Source of Learning and Development, Prentice Hall, 1984
[2]
Lehey, Greg, The Complete FreeBSD, 3rd Edition, Walnut Creek CDROM, 1999.
[3]
Eckstein, Robert, et al , Using SAMBA., O'Reilly, 2000.
Our approach has been to start small and expand as we gain experience with the laboratory equipment, and as budgets allow. We list several areas that we would like to develop in the future: • Ability to observe the electrical signals on the network. What does Manchester encoding look like? What is the voltage magnitude of an Ethernet signal? Can we see a collision? Logic analyzer or oscilloscope interfaces are required to provide access to the electrical signals. • Wireless networking technology interfaces. IEEE 802.11 and infrared links for throughput measurements and security investigations. • High-level Data Link Control (HDLC). Develop exercises to demonstrate the throughput of Stop & Wait, Go-Back-N, and Selective Reject protocols. • Perl scripts: Simplify the process of isolating and decoding the constituent parts of the TCP and IP header for observing different header contents as a function of network services. • Optical networking technologies. Add high speed optical networking technologies to analyze throughput and other metrics. • Variable time delays. Enable us to more accurately simulate wide area networks on an isolated, local network.
SUMMARY The portable laboratory provides a cost-effective solution to providing access to network equipment for hands-on experience with networking protocols in an isolated environment. Students configure network hardware, observe and measure network traffic performance, and configure network services. Through the use of the laboratory, we reinforce networking principles with practical experience 0-7803-7444-4/02/$17.00 © 2002 IEEE November 6 - 9, 2002, Boston, MA 32 nd ASEE/IEEE Frontiers in Education Conference T3D-11
